One has blended in so seamlessly you’re inclined to dial up his player profile on the Internet to see if this is his fourth or fifth NFL season.

The other has been on an island, standing alone and feeling as if his pants are down around his ankles for all to see, sometimes looking so lost you wonder if he belongs in the league.

These are the contrasting plights and paths of the Jets’ 2013 first-round draft picks:

Defensive tackle Sheldon Richardson is one of the darlings of the league, a relentless playmaker with upside that smacks scouts in the face. Through nine games, he is a favorite to win the NFL’s Defensive Rookie of the Year.

Then there is cornerback Dee Milliner, whose erratic play has gotten him benched twice and who has missed three games with a hamstring injury.

The ironic twist is Richardson, who was selected 13th overall with the Jets’ second pick in the first round, figured to be the afterthought compared to Milliner, who was chosen ninth overall and slotted to be the immediate replacement for the traded Darrelle Revis.

Richardson was supposed to be a project player who would slowly be groomed into a starter on a defensive line that was already fairly stout before his arrival, and Milliner was supposed to be the polished, ready-made starter coming from college football’s top program, Alabama.

To the surprise of virtually everyone — with the exception of the confident Richardson — the scenario has turned out to be the complete opposite.

Quietly, one of the cool behind-the-scenes stories inside the Jets locker room has been Richardson’s role in trying to lift Milliner’s confidence.

Richardson, who rooms with Milliner on the road, was the young cornerback’s biggest booster after he was torched for four pass plays for 108 yards by the Bengals in less than a half and benched two games ago. Jets coach Rex Ryan, who insisted Milliner “will be the best rookie corner by the time the season is over,’’ started him last Sunday against the Saints and he responded with his best game.

“I wanted my roommate to feel like he wasn’t the only one, that we all struggle at some point,’’ Richardson said. “The only thing I told him coming into the [Saints] game was to ‘slow it down in your mind.’ I’ve seen him play when he played against us at Missouri and he was at Alabama. I saw the confidence in his eyes back then.’’

Richardson had not seen the same swagger in Milliner as a Jet that he saw when they faced each other in college.

“You could see it in his face,” Richardson said, “frustration setting in.’’

Milliner, who said recently, “It’s just been a long season,” has been a stand-up pro while dealing with his struggles.

“I let my teammates down,” he said after the Bengals game.

“I think he knows he’s better than that,” cornerback Antonio Cromartie said. “He’s trying to live up to his first-round [status]. Just play football. He needs to get back to basics. He knows what he has to do.”

Milliner has made no excuses, but injuries have slowed his progress. He came to the Jets with a bum shoulder, which kept him from offseason practices and limited him in training camp, and then he suffered a hamstring injury that cost him three games.

“He didn’t play much in preseason, which for me is when I got my feet wet,’’ Richardson said. “That was my introduction as far as the speed and physical strength of the game in the NFL. He missed out on that a little bit, so he started behind the eight ball. I told him, ‘Don’t be surprised if you start hearing the bust word.’ You can either be a bust or a good draft pick. They like to label you like that and label you quickly.’’

Just as it’s far too early to send Richardson to Canton, it’s too early to label Milliner a bust. Both would be irresponsible, knee-jerk reactions to less than three months of football.

The Jets’ new backup quarterback, veteran David Garrard, whose locker is just a couple stalls from Richardson’s, said he “had to ask Sheldon what year he was in when I first got here,’’ because he thought the rookie was a veteran.

Richardson said he “takes it as a compliment’’ when told he carries himself like a veteran.